The known simplest technique of accomplishing a multicolor printing is to use a tandem arrangement of a number of single color printing units which are equal in number to the number of colors desired and which are coupled together by a plurality of transfer cylinders. In such an arrangement, each of the printing units includes a plate cylinder, a blanket cylinder and an impression cylinder which are sequentially in bearing engagement. In one example, a single transfer cylinder is provided between adjacent printing units, and in another example, as many as three transfer cylinders may be provided (see FIG. 1). Where such single color printing units are used, a paper to be printed is initially fed from a paper feeder to the impression cylinder of a first printing unit and thence to the grippers thereof, and subsequently passed to the grippers of a transfer cylinder. If a plurality of transfer cylinders are provided between adjacent printing units, the paper will be successively passed to the grippers of the respective transfer cylinders before it is introduced onto the impression cylinder of a second printing unit. After passing through a plurality of printing units, the paper finally reaches the grippers of a delivery. Thus, before the printing process is completed, the paper will experience a number of passes represented as n + T(n - 1) where n represents the number of printing units used and T the number of transfer cylinders located between adjacent printing units. It is readily seen that an increase in the number of passes results in a decrease in the registering accuracy. Where single color printing units are used, the only way to reduce the number of passes is to reduce the number of transfer cylinders provided between adjacent printing units. While it will appear that a single transfer cylinder may be used to achieve the coupling between adjacent printing units, this is not always practicable in the actual design. This is because either the single transfer cylinder must have its diameter increased greater than that of the impression cylinder (FIG. 2), or its diameter must be greater than that of both the impression and blanket cylinders (FIG. 3), but this results in an increased cost and an increased size of the entire framework. It is known that an increased diameter is required for the transfer cylinder in order to provide a certain spacing between adjacent printing units so as to facilitate a replacement of the plate on the plate cylinder, servicing of an inking system and a dampening system, and the impression throw off of the blanket cylinder.
In order to overcome such difficulty, there has been proposed a cylinder arrangement which permits a single printing unit to print in two colors. In one arrangement of this type, an impression cylinder is provided in common to two sets of plate and blanket cylinders (FIGS. 4 and 5). Each set of the plate cylinder and blanket cylinder is capable of printing in a color which is different from the color of the other set, so that a two color printing can be achieved with a single printing unit and a four color printing can be accomplished by a pair of interconnected printing units. In addition to the five cylinder arrangement mentioned above, a two color printing unit may comprise a four cylinder arrangement in which a pair of plate cylinders are engaged by a common blanket cylinder which is in turn engaged by a single impression cylinder. However, in this instance, the diameter of the impression cylinder must be reduced to one-half that of the blanket cylinder, which limits the use of such arrangement to a two color printing press. This is because a reduced diameter of the impression cylinder as compared with that of the blanket cylinder presents a difficulty in the interconnection of two printing units and also in the construction of the entire framework. A two color printing unit having the five cylinder arrangement is used not only in a two color printing press but also in a multicolor press capable of printing in four or more colors. However, in the prior art practice, the impression cylinder has the same diameter as the blanket cylinders and the plate cylinders, with the cylinder arrangement in a single printing unit being V-shaped either in vertical or horizontal position. When interconnecting a plurality of printing units, two methods are known. In a first method, transfer cylinders are provided between adjacent units as in the case of using single color printing units (FIG. 4), and in a second method, a chain conveyor having grippers is provided therebetween (FIG. 5). When the first method is employed, it will be desirable to provide a single transfer cylinder in order to reduce the number of passes, but this cannot be attained since a greater spacing is required between adjacent printing units in the cylinder arrangement of this type than in a single color printing unit. According to the second method, the chain conveyor running across the adjacent printing units would represent a single transfer cylinder, but locating a number of grippers very accurately on the chain conveyor involves a machining difficulty. In addition, a slack in the chain causes an error which must be compensated for.
Viewed from another standpoint, the known five cylinder arrangement having a common impression cylinder bearing against a pair of blanket cylinders (FIGS. 4 and 5) has another disadvantage of being susceptible to a mackle phenomenon in color since the equality of the diameter between the blanket cylinders and the impression cylinder results in inks of different colors being simultaneously applied to a paper on the impression cylinder from the respective blanket cylinders. This results from a very slight difference in the size of the two blanket cylinders and also from a differential elastic deformation of the respective blanket cylinders as a result of differential bearing pressures with the impression cylinder.
A further significant disadvantage found in the prior art, whether single color printing units or two color printing units are combined together, is the fact that the respective printing units must be independently driven from a common drive source. Although two single color printing units may sometimes be driven simultaneously, where four units are used, they must be separately driven in groups of two units. This is because several transfer cylinders or chain conveyors must be disposed between the driven parts of the respective printing units, but the transmission of the power through the parts in a sequential manner prevents the synchronization from being maintained as a result of transmission loss. If a drive shaft extending below the respective printing units is used to transmit the power to the driven parts of the respective units through suitable gearing, there can be a substantial relative play between the respective gearings, and in addition the torsional loss of the drive shaft must be taken into consideration. To avoid such difficulties, a complex gearing such as shown in Japanese Pat. Publication No. 11367/63 had to be used heretofore.